Thin-walled steel casting and method of making same



- Patented Oct. 18, 1938 UNITED STATES.

v 2,133,532 THIN-WALLED STEEL CASTING AND METHOD OF MAKING SAME AlfredL. Boegehold, Detroit, Mich., assignor to General Motors Corporation,Detroit, Mich., a corporation of Delaware No Drawing.

4 Claims.

This invention relates to a metallurgical process and more particularlyto a thin-walled ferrous metal casting and method of making same.

There are numerous places where a thinwalled ferrous metal or steelcasting of intricate shape is desired. Where the shape is quitecomplicated it becomes too expensive to fabricate the shape from steelstampings either as a whole or made up from individual stampings copperbrazed together. It is an object of this invention to provide a new andimproved thin-walled article and method of making same.

A specific object of my inventtion is to provide a thin-walled ductilesteel casting of intricate shape from a ferrous metal casting of highcarbon content in which there is no free carbon.

Another object of my invention is to provide a thin-walled ductileferrous metal casting which may be heated to high temperatures withoutbecoming mushy or without any permanent change in dimension.

In carrying out my invention I first cast a thin-walled article ofdesired shape of a high carbon content cast iron of such compositionthat the casting contains no free carbon. The fluidity of such a highcarbon composition permits casting in very thin sections.

One specific example of a high carbon iron that may be used in carryingout my new and improved process is as follows:

Percent Carbon 3.50

Manganese 1.00 Silicon 1.00 Sulphur and phosphorus low, e. g. less than..10 Iron Balance I do not wish to be limited to this compositionas othercompositions may be used so long as the metal has suflicient fluidity tobe cast into thin sections and so long as the composition is one inwhich substantially no free-carbon will be present in the casting. Ingeneral, a range of 2.5% to 4.3% carbon may be used.

After making the thin-walled casting it is decarburized so that aductile ferrous metal or low carbon steel casting results. Thedecarburizetion is preferably accomplished by subjecting the casting tothe influence of moist hydrogen or other highly decarburizing gas at ahigh temperature for a period of time sufficient to completelyor'substantially completely decarburize the casting. The use of moisthydrogen at a high temperature enables the decarburization to 55 takeplace rapidly and thus attain the desired Application June 15, 1936,Serial No. 85,331

result before graphitization precipitates any free carbon in thecasting. The temperature of the moist hydrogen may preferably be withinthe range 1600-2000 F.

The time necessary to decarburize the casting will vary with thethickness of the walls and the temperature of the moist hydrogen orother decarburizing gas. As an example, a section .030 inch thick willbecome decarburized in the presence of moist hydrogen at 1800 F. inabout two hours.

In order to facilitate the rate of decarburization during the hydrogentreatment acertain amount of vanadium may be added. For example, amountswithin the range 35% to .55% may be used. The vanadium will have theadditional advantage of improving the physical properties of the finalproduct by preventing the formation of any primary graphite in the metalas cast.

The result of decarburizing the high carbon ferrous metal casting willbe a ductile ferrous metal or steel casting containing neither freecarbon nor suflicient combined carbon to make it brittle. Such castingsmay be used, for example, for copper brazing to other steel partswithout such change in shape or dimensions as to interfere with thebrazing operation. Temperatures up to 2100 F. may be used without thearticle becoming mushy or without any permanent change in dimensions,such as would be the case with cast iron or malleable iron articles.

It will be understood that thin-walled articles of many different shapesmay be made by my process and that many changes not specificallyenumerated may be made without departing from the spirit of my inventionand therefore I do not wish to limit the patent granted thereon exceptas necessitated by the prior art.

I claim:

1. The method of making a thin-walled ductile ferrous metal article ofsheet metal thickness which comprises subjecting a thin-walled ferrousmetal casting of sheet metal thickness of high carbon content having nofree carbon and having vanadium present within the range 35% to .55% tothe influence of a decarburizing gas at a high temperature until thecasting contains substantially no combined carbon and no free carbonwhereby the article may be heated up to 2100" F. without becoming mushyor undergoing permanent change in dimensions.

2. The method of making a thin-walled ferrous metal article whichcomprises providing a thinwalled casting of sheet metal thickness ofapproximately the following composition: 3.50%

carbon, 1.00% manganese, 1.00% silicon, .35 to 55% vanadium, less than10% sulphur and phosphorus and the balance iron, said casting having itscarbon all in combined form, and then decarburizing said casting bysubjecting the same to the influence of moist hydrogen at a temperaturewithin the range of 1600-2000 F. until the article containsapproximately no combined carbon and contains no free carbon whereby thearticle may be heated up to 2100 F. without becoming mushy or undergoingpermanent change in dimensions.

3. The method of making a thin-walled ferrous metal article whichcomprises providing a casting having a wall of approximately .03 inthickness of substantially the following composition: 3.50% carbon,1.00% manganese, 1.00% silicon, .35 to 55% vanadium, less than .10%sulphur and phosphorus and the balance iron, said casting having itscarbon all in combined form, and decarburizing said casting bysubjecting said casting to the influence of moist hydrogen at atemperature within the range of l600-2000 F. until said casting containssubstantially no combined carbon and contains no free carbon whereby thearticle may be heated up to 2100 F. without becoming mushy or undergoingpermanent change in dimensions.

4. As a new article of manufacture, a casting having walls of sheetmetal thickness of ductile, ferrous metal containing vanadium and havingno free carbon and approximately no combined carbon whereby the articlemay be heated up to 2100 F. without becoming mushy or undergoingpermanent change in dimensions, said casting having been formed bydecarburizing substantially completely a casting having walls of sheetmetal thickness of high carbon content cast iron containing no freecarbon and having 35% to .55% vanadium, the decarburization having beencarried out by subjecting the casting to the presence of moist hydrogenat a temperature within the range l600-2000 F.- for a time sufficient todecarburize substantially completely the thin walled casting.

ALFRED L. BOEGEHOLD.

